JPH06192573A - Polyimide-based rein composition for sliding material - Google Patents

Abstract

PURPOSE:To obtain a composition, composed of a specific polyimide resin, specified graphite, tetrafluoroethylene resin and a cured powdery phenolic resin and excellent in heat resistance, sliding characteristics and abrasion resistance under sliding conditions of a high PV value. CONSTITUTION:The composition is obtained by blending 100 pts.wt. resin composition composed of (A) 50-90wt.% thermoplastic polyimide resin expressed by formula I (X is 1-10C hydrocarbon, thio, etc.; R1 to R4 are H, lower alkyl, etc.; Y is >=2C tetravalent group such as an aliphatic or aromatic group) and (B) 50-10wt.% graphite, prepared by graphitizing a nonphenolic resin-based raw material and having >=97% fixed carbon content with (C) 5-20 pts.wt. tetrafluorothylene resin (preferably the resin of a powdery form) and (D) 5-30 pts.wt. cured powdery phenolic resin. Furthermore, the component (A) is preferably prepared by reacting an aromatic ether diamine expressed by formula II with a tetracarboxylic dianhydride and cyclodehydrating the resultant polyamic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide resin composition for a sliding material which is applied under sliding conditions where a high load is required mechanically and thermally.

[0002]

2. Description of the Related Art Polyimide resins have excellent heat resistance, and their properties have been improved so that they can be used as a sliding material under severe conditions such as high temperature, high load and high speed sliding.

For example, as a technique for improving the sliding characteristics of polyimide resin, Japanese Patent Laid-Open No. 63-8455 discloses:
It is described that a tetrafluoroethylene resin is added to a polyimide resin. Further, JP-A-63-314712 discloses that abrasion resistance is improved by adding a phenol resin cured product together with a tetrafluoroethylene resin to a polyimide resin.

[0004]

However, a conventional polyimide-based resin composition for a sliding material obtained by adding a phenol resin cured product together with a tetrafluoroethylene resin to a polyimide resin has a glass transition temperature (Tg = 240
℃), for example, 640 kg / cm ² -m /
There is a problem that abrasion resistance is low when sliding at a high PV value such as min.

In order to improve the wear resistance under the above-mentioned severe sliding conditions, a method of subjecting a thermoplastic polyimide resin to a heat treatment to obtain a crystallinity of 25% is also known. However, in this case, since the molded product shrinks by 2 to 5% (shrinkage rate) before and after the crystallization treatment, it is not possible to obtain a molded product with good dimensional accuracy.

As a technique for reducing the shrinkage ratio before and after the crystallization treatment, JP-A-4-175373 and JP-A-4-202470 describe adding a thermotropic liquid crystal polymer. ing. The liquid crystalline polymer used in this case is highly oriented to reduce the linear expansion coefficient of the molded product and improve the dimensional accuracy of the molded product.

However, since the composition comprising the thermotropic liquid crystal polymer and the thermoplastic polyimide resin is an incompatible system, the wear resistance can hardly be improved.

Therefore, the present invention solves the above-mentioned problems and provides a polyimide resin composition for a sliding material, which has excellent heat resistance and sliding characteristics, and has an abrasion resistance under sliding conditions of a high PV value. In addition to having excellent properties, it is an object to make the shrinkage rate smaller before and after the crystallization treatment and to easily manage the dimensional accuracy.

[0009]

In order to solve the above-mentioned problems, in the present invention, it is obtained by graphitizing 50 to 90% by weight of a thermoplastic polyimide resin represented by the following formula and a non-phenol resin raw material. 5 to 20 parts by weight of a tetrafluoroethylene resin and 5 to 30 parts by weight of a powdered phenol resin cured product, to 100 parts by weight of a resin composition consisting of 50 to 10% by weight of graphite having a fixed carbon amount of 97% or more. Was compounded.

Note

[0011]

[Chemical 2]

The graphite having a fixed carbon content of 97% or more may be scaly natural graphite. The details will be described below.

First, the thermoplastic polyimide resin represented by the above formula 2 used in the present invention is obtained by the reaction of one or more tetracarboxylic dianhydrides with the aromatic ether diamine represented by the following formula 3. It is obtained by dehydration cyclization of polyamic acid.

[0014]

[Chemical 3]

Among such polyimide resins, commercially available polyimide resins (R _{1 to} R ₄ in the above formula 2) are used.
Are all hydrogen), manufactured by Mitsui Toatsu Chemicals Inc .:
AURUM is mentioned.

Next, the fixed carbon amount in the present invention is 97%
The above graphite may be natural flake graphite produced from the ground or artificial graphite. Out of natural graphite
Experiments have shown that scaly graphite having an average particle size of about 10 μm is particularly preferable for achieving the intended purpose of the present invention. The artificial graphite is preferably, for example, one in which coke derived from pitch is solidified with tar or pitch, baked at about 1200 ° C., placed in a graphitizing furnace, and crystals are grown at a high temperature of about 2300 ° C. In addition, as a raw material of artificial graphite, pitch, coal tar, coke, wood raw material, furan resin,
Polyacrylonitrile is used, and phenol resin is not used as a raw material. This is because it is not preferable to use it together with a phenol resin cured product added separately.

Here, the fixed carbon in the graphite component is the remaining component obtained by quantitatively removing water, ash and volatile matter in the industrial analysis of the coal test method, and a small amount of hydrogen containing carbon as the main component, It contains oxygen and nitrogen. When the fixed carbon content is less than 97%, satisfactory results cannot be obtained for both wear resistance and shrinkage of the molded product before and after the crystallization treatment.

The mixing ratio of the above-mentioned thermoplastic polyimide resin and graphite is 50 to 90% by weight of the thermoplastic polyimide resin and 50 to 10% by weight of graphite having a fixed carbon amount of 97% or more. This is because if the amount of graphite added is more than 50% by weight, the melt viscosity of the composition becomes large and melt molding becomes difficult, and if it is less than 10% by weight, the effect of improving wear resistance cannot be sufficiently obtained. Because.

Next, the tetrafluoroethylene resin used in the present invention is preferably in the form of powder so as to be uniformly mixed in the composition. For example, molding powder, fine powder, or γ-rays after molding and firing can be used. It may be pulverized by electron beam irradiation. The blending ratio of the tetrafluoroethylene resin is 5 to 20 parts by weight based on 100 parts by weight of the composition of the thermoplastic polyimide resin and graphite. Because, if the amount is less than 5 parts by weight, the added thermoplastic polyimide resin composition does not have sufficient sliding properties, and if the amount exceeds 20 parts by weight, the mechanical strength inherent to the thermoplastic polyimide resin is impaired. Because.

The powdery phenolic resin cured product used in the present invention comprises a novolac-type or resol-type phenolic resin produced by using a formalin-generating compound for phenols, if necessary, containing a known filler, and as it is. Alternatively, it may be obtained by adding a crosslinking agent such as hexamine and heating it to obtain a cured product, which is then crushed. The manufacturing method is disclosed in JP-A-57-17701 and JP-A-58-1.
As disclosed in Japanese Patent No. 7114 and the like, examples of commercially available products include Bell Pearl manufactured by Kanebo Co., Ltd.

Here, these phenolic resins are heat infusible powdery resins, and specifically have an average particle size of 50 μm.
The particle size is preferably m or less, and 80% by weight or more and 150 μm or less. This is because when the particle size is larger than 150 μm, the mutual adhesion of the powder particles to each other is insufficient at the time of molding, and the mechanical strength such as wear resistance and bending strength of the molded article decreases. This is because it is not preferable. And, the phenol resin cured product used in the present invention is required to be sufficiently cured. For example, when the degree of curing is used as a scale to display the solubility in methanol,
Its solubility is 20% by weight or less, preferably 15% by weight or less, and more preferably 5% by weight or less. This is because when the solubility of methanol exceeds 20% by weight, foaming occurs during molding, resulting in voids and microcracks in the molded body.

The compounding ratio of such a phenol resin cured product is 5 to 30 parts by weight with respect to 100 parts by weight of the composition comprising the thermoplastic polyimide resin and the graphite. This is because, if the amount is less than 5 parts by weight, the effect of abrasion resistance cannot be obtained, and if the amount is more than 30 parts by weight, not only the melt viscosity of the composition becomes high and melt molding is not possible, but also the friction coefficient cannot be reduced. is there.

The polyimide resin composition for a sliding material according to the present invention may contain various known additives listed in the following items within the range not impairing the object of the present invention. Of course.

That is, as a reinforcing agent, glass fiber,
Carbon fibers, boron fibers, silicon carbide fibers, carbon whiskers, asbestos, metal fibers, rock wool, etc. Flame retardant improvers such as antimony trioxide, magnesium carbonate, calcium carbonate, etc. Electrical property improvers such as clay, mica, etc. , Asbestos, silica, graphite, etc. as cracking resistance improver, iron, zinc, aluminum, copper and other metal powders as thermal conductivity improver, other fillers such as glass beads, glass balloons, calcium carbonate, alumina, Talc, diatomaceous earth,
Hydrated alumina, shirasu balloon, various metal oxides, inorganic pigments, etc., which are natural or synthetic compounds stable at 300 ° C. or higher.

When a thermotropic liquid crystal polymer having the basic structure of (II) to (IV) of the following chemical formula 4 is added as an additive other than the above, the flowability at the time of melt molding and the crystallization at the time of crystallization are improved. The contraction rate can be relaxed.
However, this compound has an adverse effect of impairing the wear resistance as described above, so that the compounding ratio thereof is preferably 2 to 5 parts by weight.

[0026]

[Chemical 4]

The means for mixing the raw materials used in the present invention described above is not particularly limited, and the raw materials may be individually supplied to the melt mixer, or a Henschel mixer, a ball mixer, a ribbon blender in advance. Two or more types may be simultaneously mixed using a general-purpose mixer such as. The mixing temperature in that case is usually 250 to 420.
C., preferably 300 to 400.degree. Further, as the molding method, compression molding, sinter molding or the like can be adopted, and injection molding or extrusion molding can be performed by forming a homogeneous melt blend.

[0028]

The polyimide resin composition for sliding materials according to the present invention uses a heat-resistant polyimide resin as a matrix, and a tetrafluoroethylene resin, which is particularly excellent in the effect of reducing the friction coefficient, is added to the matrix. It has excellent heat resistance and friction characteristics, and by adding a certain amount of powdered phenolic resin cured product and a certain amount of graphite with a fixed carbon content of more than a certain amount, wear resistance is improved and before and after crystallization treatment. The shrinkage rate is small.

[0029]

[Examples] The raw materials used in Examples and Comparative Examples are summarized below. All the blending ratios were% by weight, and the abbreviations were shown in [].

(1) Thermoplastic polyimide resin [TPI] manufactured by Mitsui Toatsu Chemicals Inc .: AURUM # 450 (2) Flake natural graphite [scaly graphite] manufactured by Nippon Graphite Co., Ltd .: ACP (fixed carbon content 99.5%) (3) Artificial graphite [Round graphite] LONZA: KS10 (fixed carbon amount 99.5%) (4) Soil-granular graphite [soil-granular graphite] Nippon Graphite: blue P (fixed carbon amount 92.5%) (5) Thermotropic liquid crystal polymer [LCP] Sumitomo Chemical Co., Ltd .: Econol E5000 (6) Phenolic resin cured product [PF-1] Kanebo: Bell Pearl C2000 (average particle size 48 μm) (7) Powder phenol Resin cured product [PF-2] Kanebo Co., Ltd .: Bell Pearl R900 (average particle size 22 μm) (8) Tetrafluoroethylene resin [PTFE] Kitamura Co., Ltd .: KTL610 [Examples 1-8, comparison 1-8] After mixing dry blended in proportions shown in Table 1 or Table 2 raw materials, extruded and granulated under the conditions of three hundred and seventy to four hundred ° C. using a twin-screw melt extruder,
The pellets obtained are supplied to an injection molding machine, the cylinder temperature is 370 to 400 ° C., the injection pressure is 1000 kg / c.
m ^2, by injection molding at a mold temperature of 150 to 200 ° C.,
A test piece was molded. For the obtained test pieces, (1) friction coefficient, (2) wear coefficient, (3) critical PV value, (4) flexural modulus, (5) dimensional change due to crystallization treatment were measured by the following methods, respectively. The obtained results are shown in Table 3 or Table 4.

(1) Friction coefficient Using a thrust type friction / wear tester (made by our company), surface pressure 5.0 kg / cm ² , sliding speed 128 m / min, mating material S
UJ2, non-lubricated, and the friction coefficient at the time of 60 minutes of operation was determined.

(2) Wear coefficient × 10 ⁻¹⁰ Using the tester used for measuring the friction coefficient, the surface pressure was 5.0 k
g / cm ² , sliding speed 128 m / min, mating material; SUJ
2. The wear coefficient (cm ³ / kgf · m) was determined from the wear test results in the non-lubricated state, the amorphous state after 100 hours of operation, and the state after the crystallization treatment.

(3) Limit PV value In the above abrasion test, the sliding speed was 128 m / min, the mating material was SUJ2, no lubrication, and the limit PV value after crystallization treatment for 100 hours of operation (kg / cm ² -m / min) )
I asked. However, the wear coefficient is 100 × 10 ^-10 cm ³
The surface pressure of not less than / kgf · m was defined as the limit PV.

(4) Flexural Modulus The flexural modulus (kgf / cm ² ) at room temperature and 230 ° C. was determined according to ASTM-D790. (5) Dimensional change due to crystallization treatment Thrust washer test piece with an outer diameter of 66.5 mm, an inner diameter of 37 mm, and a thickness of 2 mm (from the center of the inner diameter to a gate port diameter of 2.5 m
Disc gate molding with m and cutting the inner diameter)
Using 20 pieces, step heating to these at 320 ° C,
The crystallization treatment was performed for 2 hours. Then, the presence or absence of warpage was examined by (a) outside diameter standard deviation before and after treatment, (b) shrinkage ratio, and (c) visual observation.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

As is clear from the results of Tables 3 and 4, Comparative Examples 1 to 3 in which the powdered phenolic resin cured product was not mixed had a high wear coefficient and a fixed carbon content of 97%.
In Comparative Example 4 in which the compounding amount of graphite exceeds the predetermined range,
It could not be molded. Furthermore, Comparative Example 5 containing graphite having a fixed carbon content of less than 97% or Comparative Example 6 containing no graphite,
The dimensional change was large after the crystallization treatment. In addition, Comparative Example 7 or Comparative Example 8 containing the liquid crystal polymer was inferior in the limit PV value and the wear coefficient.

On the other hand, Examples 1 to 8 satisfying all the conditions of both the compounding ingredients and the compounding ratios have sufficiently high limit PV values of 1500 or more, and the abrasion coefficient and mechanical strength of other test items. The (bending elastic modulus) and the coefficient of friction also showed excellent characteristics as a sliding material, and in particular, the dimensional change after the crystallization treatment was sufficiently small.

[0041]

[Effect] As described above, the present invention uses a heat-resistant polyimide resin as a matrix, and adds tetrafluoroethylene resin, which is particularly excellent in the effect of reducing the friction coefficient, to the matrix,
Furthermore, since a powdered phenolic resin cured product and a polyimide-based resin composition in which a fixed amount of graphite with a fixed carbon amount of not less than a predetermined amount is added, heat resistance, sliding characteristics, and resistance to high PV values under sliding conditions are provided. In addition to making it excellent in wear resistance,
The shrinkage rate is small before and after the crystallization treatment, and there is an advantage that the polyimide-based resin composition for a sliding material is easy to control the dimensional accuracy.

Claims (2)

[Claims] 1. A thermoplastic polyimide resin represented by the following formula in an amount of 50 to 90% by weight, and a graphite having a fixed carbon amount of 97% or more obtained by graphitizing a non-phenolic resin raw material.
Polyimide for a sliding material obtained by mixing 5 to 20 parts by weight of a tetrafluoroethylene resin and 5 to 30 parts by weight of a powdered phenol resin cured product with 100 parts by weight of a resin composition consisting of 0% by weight. -Based resin composition. Note: 2. The polyimide resin composition for a sliding material according to claim 1, wherein the graphite having a fixed carbon content of 97% or more is flaky natural graphite.